[nrf fromtree] tests: drivers: pwm: nrf54h20dk: add memory-region prop

This property will ensure that PWM driver allocates data buffer
in appropriate location.

Signed-off-by: Nikodem Kastelik <[email protected]>
(cherry picked from commit 539a428)

tests/drivers/pwm/pwm_api/boards/nrf54h20dk_nrf54h20_cpuapp.overlay

@@ -17,4 +17,5 @@
 	pinctrl-0 = <&pwm_default>;
 	pinctrl-1 = <&pwm_sleep>;
 	pinctrl-names = "default", "sleep";
+	memory-regions = <&cpuapp_dma_region>;
 };